$ \left(\dfrac{81}{256}\right)^{-\frac{1}{4}}$
Answer: $= \left(\dfrac{256}{81}\right)^{\frac{1}{4}}$ Figure out what goes in the blank: $\Big(? \Big)^{4}=\dfrac{256}{81}$ Figure out what goes in the blank: $\Big({\dfrac{4}{3}}\Big)^{4}=\dfrac{256}{81}$ So $\left(\dfrac{81}{256}\right)^{-\frac{1}{4}}=\left(\dfrac{256}{81}\right)^{\frac{1}{4}}=\dfrac{4}{3}$